1. Field of Invention
The field of the invention is diode laser systems used for medical or cosmetic treatments in the thermal regime alone or in conjunction with other therapies such photodynamic therapy, chemotherapy or radiation therapy.
2. Information Disclosure Statement
A lot of different tumor types, located in various parts of the body have been successfully treated with lasers in the recent years. In this way, lasers have also been used for the thermal destruction of tumors. This therapy is called laser-induced interstitial tumor therapy (LITT). The target tissue (a tumor) is irradiated with laser light using a specially designed light guide ending in an adequate applicator (e.g. cooled optical diffuser).
The light generated by a laser is absorbed selectively by tissue, because of its monochromatic and coherent nature. This absorption is dependent on the physical properties of the tissue, which include absorption and scattering. These properties depend on the wavelength of the incident laser light. Absorption in tissue is mainly characterized by water absorption, because in the infrared region there is a very large and sharp vibrational absorption band for water.
The laser light absorbed by the tissue is leading to heating of the target volume. The resulting thermal damage leads to the destruction of the tumor. The primary effect here is the direct coagulation of the irradiated tissue, while temperature dependent, also other mechanisms are described (e.g. hyperthermia).
Up to now the therapy was conducted with Nd-YAG lasers. This laser was used because there is a local absorption minimum in water at 1050 nm. At this wavelength the laser light is absorbed mainly by blood and not by water. This leads to a penetration depth, which is sufficient for a successful therapy. This means that the laser light penetrates a certain depth into the tissue before it is absorbed. Although the Nd-YAG laser is commonly used for interstitial tumor therapy, the use of this single wavelength is based primarily on the fact, that no other lasers in this wavelength range were available. Additionally this type of laser requires a lot of maintenance and costly techniques.
Due to new developments this limited approach can be overcome. Diode laser light sources will now be available in the wavelength range of 1000 nm up to 1300 nm. These laser are almost maintenance free and easy to use.
Additionally studies based on recent measurements surprisingly show that the maximum penetration depth is not located at a wavelength of 1064 nm, but in the wavelength range of 1100 nm to 1150 nm. These measurements take into account, that the penetration depth is not only dependent on the absorption of water. For this the absorption and scattering of the other ingredients of tissue also have to be taken into account. A measurement of the absorption and scattering properties of tissue (for example in brain tumors as described below) show that the penetration depth in the entire wavelength range of 1000 nm up to 1300 nm is similar to that at 1064 nm with a maximum from 1100 nm to 1150 nm. Consequently these wavelengths are also very suitable to be used for the LITT. This wavelength region has not been used in the prior art, because no adequate laser light sources (with powers of 30 W cw) were available until now.
Large penetration depths are especially important for cooled LITT (U.S. Pat. Nos. 5,989,246 and 5,861,020). These systems are used to cool the area surrounding the applicator. Therefore, a larger power can be applied without inducing carbonization or vaporization in this area. This results in even bigger lesion sizes. Having maximum penetration depths would thus help treat large areas, quicker and with less treatments.
During the coagulation process the denaturation of the proteins leads to a change of the physical properties (optical, thermal, perfusion, . . . ). Usually the denaturation leads to higher scattering and lower absorption in tissue. This means that the penetration depth will change. A large penetration depth could then be achieved by increasing the wavelength of the used laser. Therefore, it may be required to change the laser wavelength, as a consequence of the coagulation process.
The limitation to only one wavelength, in the current art, presents a number of drawbacks. The Nd-YAG equipment used by physicians in the clinics today are quite bulky and require a lot of maintenance. Moreover the laser and the wavelength used right now does not allow the maximal penetration depth, which could be achieved with laser diodes. Additionally by adjusting the wavelength one would be able to adapt to the different optical properties of different tissue types, and thereby achieve the best success in therapy. Having multiple wavelengths available in a compact diode laser package would allow the possibility of a combination with other existing therapies which could lead to new therapeutic techniques. Thus far however diode lasers operating above 1000 nm have not been available.
It is therefore an object of this invention to provide a novel family of laser systems comprising diode lasers or diode lasers with other solid state lasers for performing medical or cosmetic procedures such as Laser-induced Interstitial Tumor Therapy (LITT) treatments on large tumors or ones needing high penetration depths, and which can operate at more than one wavelength in the wavelength range of 1000 nm to 1300 nm and more optimally between 1100 to 1300 nm.
It is another object of this invention to provide diode laser systems with at least two emitters or emitter groups, each of which is coupled to an optical fiber or waveguide.
A further object of this invention is to provide a diode laser system where each single emitter or emitter group can be individually controlled in power.
A still further object of this invention is to incorporate within the system means to provide active tissue cooling at the distal end of the fibers or waveguides and/or to provide individual feedback loops for each single emitter or emitter group to control and stabilize the temperature induced in the tissue.
Yet another object of this invention is to provide a method for a surgical or cosmetic laser procedure, such as laser-induced interstitial tumor therapy, using a diode laser system operating at wavelengths between 1000 nm and 1300 nm and where delivery to interior sites employs interstitial fibers or waveguides.
Still another object of this invention is to provide a method for a surgical or cosmetic laser procedure which can be combined with chemotherapy or radiation therapy to enhance the therapeutic effects of both therapies.
Another object of this invention is to provide a laser system which can be tuned to the absorption band of an absorber, which has been introduced to the treatment site prior to irradiation.
Briefly stated the present invention provides laser systems for medical or cosmetic applications, comprising diode lasers or diode lasers with other solid state lasers which can deliver up to 30 cw or more, and which generally operate at more than wavelength within the range of 1000 to 1300 nm. Individual emitter or emitter groups within the diode laser system can be powered independently. These laser systems provide maximum penetration depths for procedures such as Laser-induced Interstitial Tumor Therapy, alone or in conjunction with other therapies such as PhotoDynamic Therapy, chemotherapy, or radiation therapy. Where beneficial for the procedure, the operating wavelength of the system can be changed without interruption. In some variants, active tissue cooling at the distal end of the delivery fibers is incorporated as well as individual feedback loops to control and stabilize the temperature induced in the tissue. To enhance thermal or photo effects and thereby increase efficiencies, absorbers can be administered and the laser system tuned to the specific absorption band of the absorber.
The above, and other objects, features and advantages of the present invention will become apparent from the following detailed description read in conjunction with the accompanying drawings.